Based on a prior observation, a call$-$center management estimates that, on average, a call takes $4$ minutes to complete and there are, average, $12$ calls arriving in a $60-$minute period. What will be the service time, interarrival time and utilization of this call center?

$1.$ Interarrival time?

$2.$ Utilization $\backslash$rho $?$